1. Field of the Invention
This invention relates to a process for the direct oxidative carbonylation of lower alkanes to acids having one greater carbon atom than the alkane. The process proceeds under mild conditions in aqueous media using oxygen as the oxidant. The process is especially effective for the conversion of methane to acetic acid. The process of this invention is carried out under mild temperature conditions involving the reaction of a lower alkane, carbon monoxide and oxygen in aqueous media with a metal salt catalyst promoted by halide ions and/or a metal to produce acid having one more carbon atom than the reactant alkane.
2. Description of Related Art
A number of processes for oxidation of unsaturated hydrocarbons are known, for example: U.S. Pat. No. 3,284,492 teaching oxidation of a ozone-organic compound adduct in an aqueous alkaline hydrogen peroxide solution to produce, from olefins having terminal unsaturation, formic acid plus the acid having one less carbon atom than the original alkene; U.S. Pat. No. 4,739,107 teaching reaction of an unsaturated hydrocarbon, alcohol and CO over Pd or Pt at 20.degree. to 200.degree. C. with O.sub.2 optionally present, to form dicarboxylate esters; U.S. Pat. Nos. 4,681,707 and 4,665,213 teaching similar reactions as the 4,739,107 patent with the additional requirement of the catalyst including copper, and teaching substitution of water for the alcohol reactant to produce the corresponding carboxylic acids; U.S. Pat. No. 4,414,409 teaching reaction of an unsaturated hydrocarbon, carbon monoxide and a hydroxylic compound in the presence of a catalyst of an organic phosphine liganded palladium compound and perfluorosulfonic acid to produce corresponding acids and esters; U.S. Pat. No. 3,876,694 teaching oxycarbonylation of olefins to form corresponding acids in a nonaqueous medium using. a catalyst system of aluminum, boron or an alkaline earth metal and a compound of palladium which is soluble in the reaction medium; and U.S. Pat. No. 4,469,886 teaching hydrocarboxylation of propylene with carbon monoxide and water to produce isobutyric acid using a catalyst of palladium, a phosphoamine promoter ligand compound and a hydrogen halide.
Catalytic oxidation of saturated hydrocarbons, such as alkanes, requiring C--H activation is a very different and difficult chemical challenge, and one of great practical importance. The lower alkanes of 1 to about 6 carbon atoms are most abundant and least reactive of the alkanes, with methane being the most abundant and least reactive, having a C--H bond energy of 104 kcal/mol, with ethane being second in both categories. A number of processes have been described for such oxidations but they each suffer from requirement of high temperature and/or low turnovers of less than about 10: Baerns, M., van der Wiele, K., and Ross, J. R. H., Methane Activation--A Bibliography, Catal. Today, 4, 471-494, (1989); Pitchai, R. and Klier, K., Partial Oxidation of Methane, Catal. Rev.-Sci. Eng., 28(1), 13-88, (1986); Kung, H. H., Selective Oxidation Catalysis II, Stud. Surf. Sci. Catal., 45, 200-226, (1989); Hunter, N. R., Gesser, H. D., Morton, L. A., Yarlagadda, P. S., and Fung, D. P. C., Methanol Formation at High Pressure by the Catalyzed Oxidation of Natural Gas and by the Sensitized Oxidation of Methane, Appl. Catal., 57, 45-54, (1990); Burch, R., Squire, G. D., Tsang, S. C., Direct Conversion of Methane into Methanol, J. Chem. Soc., Faraday Trans. 1, 85(10), 3561-3568, (1989); Kowalak, S. and Moffat, J. B., Partial Oxidation of Methane Catalyzed by H-Mordenite and Fluorinated Mordenite, Appl. Catal., 36, 139-145, (1988); Stolarov, I. P., Vargaftik, M. N., Shishkin, D. I., and Moiseev, I. I., Oxidation of Ethane and Propane With Co(II) Catalyst, J. Chem. Soc., Chem. Commun., 938-939, (1991); Vargaftik, M. N., Stolarov, I. P., and Moiseev, I. I., Highly Selective Partial Oxidation of Methane to Methyl Trifluoroacetate, J. Chem. Soc., Chem. Commun., 1049-1050, (1990); Herron, N., The Selective Partial Oxidation of Alkanes Using Zeolite Based Catalysts, New J. Chem., 13, 761-766, (1989); and Lyons, J. E., Ellis, Jr., P. E., and Durante, V. A., Active Iron Oxo Centers for the Selective Oxidation of Alkanes, Stud. Surf. Sci. Catal., 67, 99-116, (1991). The Lyons, et al reference, supra, strives to achieve a one-step route to oxidation of lower alkanes to alcohols using iron oxo complexes as catalysts. The oxidation of lower alkanes with O.sub.2 catalyzed by azide-activated Group IV(a) to VIII transition metal coordination complexes is taught by U.S. Pat. No. 4,895,682. One well known disadvantage of such coordination complexes is their tendency to degrade under oxidative conditions. Mercury catalyzed oxidation of methane to methanol under mild conditions is taught by Periana, R. A., Taube, D. J., Evitt, E. R., Loffler, D. G., Wentrcek, P. R., Voss, G. and Masuda, T., A Mercury-Catalyzed, High-Yield System for the Oxidation of Methane to Methanol, Science, 259, pp. 340-343, (1993). U.S. Pat. No. 5,220,080 teaches direct catalytic oxidation of light alkanes to alcohols using a catalyst in which chromium is chemically bound to oxygen of a metal oxide support surface. Low temperature reaction of methane with chlorine in the presence of platinum chlorides and in-situ hydrolyzation of the formed methyl chloride to methanol is taught by Horvath, I. T., Cook, R. A., Millar, J. M. and Kiss, G., Low-Temperature Methane Chlorination with Aqueous Platinum Chlorides in the Presence of Chlorine, Organometallics, 12, pp. 8-10, (1993). Catalytic oxidation of ethane to acetic acid at temperatures above about 250.degree. C. using promoted vanadium oxide catalysts is taught by Merzouki, M., Taouk, B., Monceaux, L., Bordes, E. and Courtine, P., Catalytic Properties of Promoted Vanadium Oxide in the Oxidation of Ethane in Acetic Acid, New Developments in Selective Oxidation by Heterogeneous Catalysis; Studies in Surface Science and Catalysis, Ruiz, P and Delmon, B., Eds., Vol. 72, pp. 165-179, (1992). Conversion of lower alkanes into their corresponding esters by contact with an oxidizing agent, a strong mineral acid, and a catalyst comprising a Group VIII noble metal is taught by U.S. Pat. No. 5,233,113.
Metal catalyzed oxidation of alcohol to carboxylic acid requiring a divalent platinum complex for the initial oxidation step is taught by Sen, A. and Lin, M., A Novel Hybrid System for the Direct Oxidation of Ethane to Acetic and Glycolic Acids in Aqueous Medium, J. Chem. Soc., Chem. Commun., 6, 508-510, (1992) and Sen, A., Lin, M., Kao, L. C., and Hutson, A. C., J. Am. Chem. Soc. 114, 6385, (1992).
The partial oxidation of methane in a motored engine at 650.degree. to 800.degree. C. and under compression of 20/1 to 60/1 without any catalyst to form small amounts of oxygenated products is taught by U.S. Pat. No. 2,922,809.
Non-catalytic oxidation of a paraffin hydrocarbon of 4 to 8 carbon atoms in the liquid phase with molecular oxygen to produce lower aliphatic acids of 1 to 4 carbon atoms is taught by U.S. Pat. No. 2,926,191.
The formation of acetic acid from methane and carbon dioxide and the formation of acetaldehyde from methane and carbon monoxide by addition reactions in the presence of a metal catalyst, such as palladium or platinum or their carbonates, is taught by U.S. Pat. No. 1,916,041. It must be noted that there is no net oxidation in the reactions taught by the 1,916,041 patent. Further, the addition reactions referred to in U.S. Pat. No. 1,916,041 are thermodynamically uphill and cannot proceed except to produce trace amounts of the products as set forth by Jones, W. D., Development of Catalytic Processes for the Synthesis of Organic Compounds the Involve C--H Bond Activation, Chap. 5, 113-148, Selective Hydrocarbon Activation, Principles and Progress, Edited by Davies, J. A., Watson, P. L., Greenberg, A. and Lichman, J. F., VCH, (1990).
Methane is the most abundant of the alkanes, but is the least reactive, making its use as a reactant to produce more useful chemical products difficult to achieve. The industrial production of acetic acid from methane involves many steps under extreme reaction conditions. Wade, L. E., Gengelbach, R. B., Trumbley, J. L. and Hallbauer, W. L., Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 15, 398-415, Wiley, New York (1978); Wagner, F. S., Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 1. 124-147, Wiley, New York (1978); and Forster, D., Adv. Organomet, Chem, 17, 255-267, (1979). Reports of direct catalytic conversion of methane to acetic acid have involved use of peroxydisulphate as the oxidant. Nishiguchi, T., Nakata, K., Takaki, K. and Fujiwara, Y., Chem. Lett., 1141-1142, (1992) and Lin, M. and Sen, A., J. Chem. Soc., Chem. Commun., 892-893 (1992). Conversion of methane to acetic acid on a commercial scale currently involves three separate steps: (1) high-temperature steam reforming of methane to a 3:1 mixture of H.sub.2 and CO as taught by Wade et al, supra; (2) high-temperature conversion of a 2:1 mixture of H.sub.2 and CO to methanol as taught by Wade, et al, supra; and (3) carbonylation of methanol to acetic acid as taught by Wagner, supra, mainly through the Monsanto process as taught by Forster, supra. Carbonylation of methanol to acetic acid using a rhodium catalyst and an iodide promoter is taught by U.S. Pat. Nos. 5,258,549 and 5,286,900 and other processes for production of acetic acid are taught by U.S. Pat. Nos. 4,101,450; 4,613,693; 4,996,357; and 5,281,752. Conversion of methane to higher hydrocarbons is taught by U.S. Pat. Nos. 4,814,538; 5,024,984; and 5,087,786.
Our prior U.S. patent application, Ser. No. 08/095,945, filed Jul. 22, 1993, now allowed, and the article by Lin, M. and Sen, A., J. Am. Chem. Soc., 114, 7307-7308, 1992 describe the direct oxidation of lower alkanes by hydrogen peroxide in an aqueous medium with metallic palladium on carbon alone as a catalyst results in the oxidation of lower alkanes to their corresponding acid, such as methane primarily to formic acid.